Reuse Distance Analysis for Large-Scale Chip Multiprocessors

Multicore Reuse Distance (RD) analysis is a powerful tool that can potentially provide a parallel program's detailed memory behavior. Concurrent Reuse Distance (CRD) and Private-stack Reuse Distance (PRD) measure RD across thread-interleaved memory reference streams, addressing shared and private caches. Sensitivity to memory interleaving makes CRD and PRD profiles architecture dependent, preventing them from analyzing different processor configurations. However such instability is minimal when all threads exhibit similar data-locality patterns. For loop-based parallel programs, interleaving threads are symmetric. CRD and PRD profiles are stable across cache size scaling, and exhibit predictable coherent movement across core count scaling. Hence, multicore RD analysis can provide accurate analysis for different processor configurations. Due to the prevalence of parallel loops, RD analysis will be valuable to multicore designers. This dissertation uses RD analysis to analyze multicore cache performance for loop-based parallel programs. First, we study the impacts of core count scaling and problem size scaling on CRD and PRD profiles. Two application parameters with architectural implications are identified: Ccore and Cshare. Core count scaling only impacts cache performance significantly below Ccore in shared caches, and Cshare is the capacity at which shared caches begin to outperform private caches in terms of data locality. Then, we develop techniques, in particular employing reference groups, to predict the coherent movement of CRD and PRD profiles due to scaling, and achieve accuracy of 80%-96%. After comparing our prediction techniques against profile sampling, we find that the prediction achieves higher speedup and accuracy, especially when the design space is large. Moreover, we evaluate the accuracy of using CRD and PRD profile predictions to estimate multicore cache performance, especially MPKI. When combined with the existing problem scaling prediction, our techniques can predict shared LLC (private L2 cache) MPKI to within 12% (14%) of simulation across 1,728 (1,440) configurations using only 36 measured CRD (PRD) profiles. Lastly, we propose a new framework based on RD analysis to optimize multicore cache hierarchies. Our study not only reveals several new insights, but it also demonstrates that RD analysis can help computer architects improve multicore designs

Identifying optimal multicore cache hierarchies for loop-based parallel programs via reuse distance analysis

Understanding multicore memory behavior is crucial, but can be challenging due to the complex cache hierarchies em-ployed in modern CPUs. In today’s hierarchies, performance is determined by complicated thread interactions, such as interference in shared caches and replication and communi-cation in private caches. Researchers normally perform ex-tensive simulations to study these interactions, but this can be costly and not very insightful. An alternative is multicore reuse distance (RD) analysis, which can provide extremely rich information about multicore memory behavior. In this paper, we apply multicore RD analysis to better understand cache system design. We focus on loop-based parallel pro-grams, an important class of programs for which RD anal-ysis provides high accuracy. We propose a novel framework to identify optimal multicore cache hierarchies, and extract several new insights. We also characterize how the optimal cache hierarchies vary with core count and problem size

RDGC: A Reuse Distance-Based Approach to GPU Cache Performance Analysis

In the present paper, we propose RDGC, a reuse distance-based performance analysis approach for GPU cache hierarchy. RDGC models the thread-level parallelism in GPUs to generate appropriate cache reference sequence. Further, reuse distance analysis is extended to model the multi-partition/multi-port parallel caches and employed by RDGC to analyze GPU cache memories. RDGC can be utilized for architectural space exploration and parallel application development through providing hit ratios and transaction counts. The results of the present study demonstrate that the proposed model has an average error of 3.72 % and 4.5 % (for L1 and L2 hit ratios, respectively). The results also indicate that the slowdown of RDGC is equal to 47 000 times compared to hardware execution, while it is 59 times faster than GPGPU-Sim simulator

Tiramisu: A Polyhedral Compiler for Expressing Fast and Portable Code

This paper introduces Tiramisu, a polyhedral framework designed to generate high performance code for multiple platforms including multicores, GPUs, and distributed machines. Tiramisu introduces a scheduling language with novel extensions to explicitly manage the complexities that arise when targeting these systems. The framework is designed for the areas of image processing, stencils, linear algebra and deep learning. Tiramisu has two main features: it relies on a flexible representation based on the polyhedral model and it has a rich scheduling language allowing fine-grained control of optimizations. Tiramisu uses a four-level intermediate representation that allows full separation between the algorithms, loop transformations, data layouts, and communication. This separation simplifies targeting multiple hardware architectures with the same algorithm. We evaluate Tiramisu by writing a set of image processing, deep learning, and linear algebra benchmarks and compare them with state-of-the-art compilers and hand-tuned libraries. We show that Tiramisu matches or outperforms existing compilers and libraries on different hardware architectures, including multicore CPUs, GPUs, and distributed machines.Comment: arXiv admin note: substantial text overlap with arXiv:1803.0041

Chapter One – An Overview of Architecture-Level Power- and Energy-Efficient Design Techniques

Power dissipation and energy consumption became the primary design constraint for almost all computer systems in the last 15 years. Both computer architects and circuit designers intent to reduce power and energy (without a performance degradation) at all design levels, as it is currently the main obstacle to continue with further scaling according to Moore's law. The aim of this survey is to provide a comprehensive overview of power- and energy-efficient “state-of-the-art” techniques. We classify techniques by component where they apply to, which is the most natural way from a designer point of view. We further divide the techniques by the component of power/energy they optimize (static or dynamic), covering in that way complete low-power design flow at the architectural level. At the end, we conclude that only a holistic approach that assumes optimizations at all design levels can lead to significant savings.Peer ReviewedPostprint (published version